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In five of the past six years, the Kentucky Derby has ended up with a field of 20 horses. And the non-20 year, 19 loaded the gate.

That's why we've had winners such as Giacomo in 2005, Mine That Bird in 2009 and Super Saver in 2010. They were all great stories, but they were not great horses, certainly not the best horse in the field.

In 2005, that would have been Afleet Alex, who got caught in traffic and finished third. In 2009, it would have been most any horse other than Mine That Bird, who retired after failing to win any of his nine starts after the Derby.

Last year, the best horse was Lookin at Lucky, who got slammed into the rail early and wound up sixth.

"We just had terrible luck," said trainer Bob Baffert.

The kind of luck you're going to have with 19 other horses in the world's most famous race.

There's also a detrimental effect a 20-horse field has on the Kentucky Derby before the race is even run. And this 137th Kentucky Derby is the perfect example.

This appears to be an uninspiring crop. Or, is it simply because we don't know all that much about the 20 starters who are likely to make the famed walk-over?

After all, possible Derby contenders use fewer races to prepare for the race, but there are more prep races in which they can run. This produces a thinning effect. Trainers and owners can pick their spot, searching for a race that pays well in terms of graded earnings but doesn't present a lot of top-quality competition.

Of the 20 horses that have the graded earnings necessary to qualify for a spot in the Derby field, a dozen have won at least one Derby prep. Trouble is, for the majority of 12, that's all they've won.

Twice the Appeal won the Sunland Park Derby on March 26. Animal Kingdom won the Spiral on March 26. Pants on Fire won the Louisiana Derby on March 27. Dialed In won the Florida Derby on April 3. None of the four has raced since.

None of the four has needed another race, not when the winning purse guaranteed a Derby spot. Win and you're in.

This year's leading money winner, Uncle Mo, hasn't won a graded prep this year. His earnings are mostly from last year, when the Todd Pletcher-trained entry earned champion 2-year-old honors.

That wouldn't be the case if the field was limited to 14, same as the Preakness. Horses would have to earn more green to secure a spot, thus they would have to race more. Consequently, we would know more about their pedigrees, their connections, their weaknesses, their strengths.

And the strongest would make the field. In fact, you can make a case that in recent years the Preakness has been a much truer test of Thoroughbred greatness.

Look at the winners — Lookin at Lucky last year, Rachel Alexandra in 2009, Big Brown in 2008, Curlin in 2007, Bernardini in 2006, Afleet Alex in 2005, Smarty Jones in 2004, Funny Cide in 2003, War Emblem in 2002 and Point Given in 2001.

All but Rachel Alexandra went on to win champion 3-year-old male honors. And Rachel won champion 3-year-old filly, plus Horse of the Year honors.

The last Derby winner to be named Horse of the Year: Charismatic in 1999.

I am reminded of what Rachel Alexandra's original owner, Dolph Morrison, said when asked why he would not run his fantastic filly in the Derby.

"The Triple Crown races are to showcase the future stallions of our industry," Morrison replied.

We'd amend that to say it should showcase the best horses of the industry, with the best horse winning.